Holding grain to be dried is a necessary, widely adopted grain management practice that is incorporated into many heated-air grain drying systems. Wet grain is commonly defined as grain having a moisture content above about 14-15%. Many heated-air grain drying systems use hopper bottom grain tanks as wet grain holding bins to supply wet grain to heated-air dryers. These bins generally have storage capacity to hold wet grain for a short duration, usually less than 12 hours.
Some grain holding bins are equipped with aeration systems to move ambient air through the wet grain to prevent it from heating. Low storage capacity and short duration wet grain holding bins generally are not aerated. Consequently, all wet grain should be removed daily from these bins that are not equipped for aeration to prevent the build-up of heat in the grain, resulting in grain quality deterioration. Wet grain can be held for several days in properly aerated and managed wet grain holding bins without significantly impairing the grain's quality. The maximum storage life of grain depends on the wet grain moisture content and grain temperature. The maximum storage life for corn is well documented by research, however, the maximum storage life for other grains can be estimated, but is not well documented. It is commonly recommended that wet corn be dried after being held for one-half the maximum storage life.
Most grain harvested in the fall, such as corn, will not be harvested at a moisture content greater than 26%, and night-time temperatures during harvesting is frequently in the 50.degree. to 60.degree. F. range. When properly aerated, grain temperature will be a few degrees below the night-time ambient temperature. As indicated in the following table, wet shelled corn can be held in a properly operated and managed aerated bin up to approximately one week or longer before it is dried. Dryer and/or colder corn can be held longer.
______________________________________ Maximum Days to Hold Shelled Corn Before Drying* Shelled Corn Temperature % Moisture Content .degree.F.- 18 20 22 24 26 ______________________________________ 50 64 31 18 12 9 60 28 14 8 5 4 ______________________________________ *The figures in the table are onehalf the maximum storage life for shelle corn.
Holding up to a week or more supply of wet grain to be dried is a good grain drying system management practice. The wet grain can be dried during times when grain cannot be harvested because fields are muddy, harvesters need repair, etc. Holding wet grain up to a week or more allows heated-air grain dryers to continue operating even if grain is not being harvested.
A grain holding bin can be any facility structurally adequate to store wet grain. It is usually a hopper bottom grain tank or a cylindrical flat bottom grain storage bin. Grain is normally unloaded from the bottom of wet grain holding bins or tanks. This mode of grain unloading has a common characteristic. The grain at the top surface forms an inverted cone and the grain flow is from the inverted grain surface directly through the grain mass to the bottom grain unloading outlet. Consequently, as wet grain is loaded into the inverted grain surface, that grain flows to the bottom outlet to be removed from the container. The first wet grain loaded into the bin or tank is the last grain to be removed. Unless the wet grain containers are aerated, they should be completely unloaded daily, to prevent a build-up of heat in the wet grain that remains in the bin too long, which causes the grain to deteriorate.